Bonded nutplate rapid cure system

ABSTRACT

Systems for positioning and bonding a nutplate to a substrate having an aperture include a nutplate engagement fixture and a temperature sensor retention fixture. The nutplate engagement fixture includes a rigid tube and an elastomeric tube engaged with the rigid tube, the elastomeric tube having an elongated tube sized to provide a friction fit with the aperture and retain the elastomeric tube within the aperture. The rigid tube is operable to engage the nutplate at one end and the elastomeric tube is configured to anchor the nutplate engagement fixture at the aperture and secure the nutplate in contact with the substrate. The temperature sensor retention fixture includes a fixture body sized and configured to engage with the nutplate and at least one passageway within the fixture body sized and configured to allow a temperature sensor to be inserted or embedded therein with an end proximal a surface of the nutplate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. patent application Ser. No.16/163,179 filed Oct. 17, 2018, which claims priority to U.S.Provisional Application 62/649,649 filed Mar. 29, 2018, which isincorporated by reference herein in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with Government support under Contract NumbersFA8650-16-M-5062 and FA8650-17-C-5068 awarded by the U.S. Air ForceMateriel Command to Cornerstone Research Group Inc. The Government hascertain rights in the invention.

TECHNICAL FIELD

Embodiments described herein relate generally to rapid curing systemsfor bonding hardware to substrates or substructures and the associatedinstrumentation and fixtures.

BACKGROUND

Adhesively bonded hardware, which are fasteners such as nutplates,bushings, threaded inserts, sleeves, mounts, brackets, etc., arecommonly used to secure structural elements during installation orrepair. Bonded hardware is used on variety of systems including:aircraft, spacecraft, watercraft, automobiles, and industrial equipment.Adhesively bonded hardware is also used to join components of dissimilarmaterials or when welding or riveting is not an option. Bonded hardwaretypically experiences failure in the form of mechanical wear, structuraldeformation, or separation of the hardware from the mounting substrate(i.e., disbond).

Damaged hardware found during routine maintenance requires timelyreplacement and approved repair techniques often mandate the use ofcertified adhesives. Unfortunately, approved repair adhesives aretypically those used during original factory installation. Approvedhardware adhesives are generally two-part epoxies whose performancespecifications are determined by a lengthy cure (e.g. 24 hour) at roomtemperature. This specific curing time is necessary for the adhesive todevelop the strength required to hold the hardware in place forattaching other components (e.g., reattaching an access panel to anaircraft). This long cure time can negatively impact the system'savailability.

In the aerospace industry, nutplates are commonly used to attach toaircraft panels. In this case, the 24 hour curing time is highlyproblematic, because this long cure time can negatively impact theaircraft's availability. To expedite nutplate repair processes,supplemental heating has been considered in order to accelerate thecuring rate of adhesives. However, the accelerated cure profile must bewell controlled to achieve desired adhesive properties (e.g., tensilestrength, shear strength, peel strength, etc.) and nutplate load ratings(e.g., push-out force and maximum torque) while also preventing damageto the surrounding structure due to excessive temperature exposure.Moreover, the delivery of heat to the bonded nutplate area poses issues,because delivering heat in an aircraft environment with flammableliquids or vapors present is a potential safety hazard.

Accordingly, there is a need for improved bonded hardware cure systemscapable of delivering heat to specific localized areas to reliably andsafely reducing the adhesive cure time.

SUMMARY

Embodiments of the present disclosure meet those needs by providing abonded hardware rapid cure system that applies localized heating throughthe body of the hardware and into the adhesive bondline at a bondingsurface. More specially, the hardware that can benefit from the use ofthe currently disclosed rapid cure system to adhesively bond with astructure is a nutplate. By significantly reducing the cure time fornutplate bonding in an aircraft panel, the present systems and methodsminimize the time for nutplate installations and repair, thus increasingaircraft production rate in manufacture and reducing the unavailabilityfor an aircraft during maintenance. In addition, the currently disclosedsystem also allows better control of the cure temperature at thebondline and the bonding surface of the nutplate, leading to improvedconsistency of the adhesive cure and bonded nutplate performance.

According to one embodiment of the present disclosure, a nutplateengagement fixture for temporarily securing a nutplate in a system forpositioning and bonding a nutplate to a substrate comprising at leastone aperture is provided. The nutplate engagement fixture comprises arigid tube comprising a first section having a first diameter and asecond section having a second diameter, the first diameter beinggreater than the second diameter. The nutplate engagement fixturefurther comprises an elastomeric tube engaged with the rigid tube at thesecond section of the rigid tube, the elastomeric tube comprising anelongated tube with an external diameter sized to provide a friction fitwith the aperture and retain the elastomeric tube within the aperture.The rigid tube is operable to engage the nutplate at one end and extendthrough the aperture of the substrate. Further, the elastomeric tube isconfigured to anchor the nutplate engagement fixture at the aperture andsecure the nutplate in contact with the substrate.

According to a further embodiment, a temperature sensor retentionfixture for temporarily securing at least one temperature sensor to anutplate in a system for positioning and bonding a nutplate to asubstrate comprising at least one aperture is provided. The temperaturesensor retention fixture comprises a fixture body sized and configuredto engage with the nutplate and at least one passageway provided withinthe fixture body of the temperature sensor retention fixture. Thepassageway is sized and configured to allow a temperature sensor to beinserted or embedded therein with an end of the temperature sensorpositioned proximal a surface of the nutplate.

These and other embodiments are described in more detail in thefollowing Detailed Description.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description of specific embodiments of thepresent disclosure can be best understood when read in conjunction withthe following drawings, where like structure is indicated with likereference numerals.

FIG. 1 is a cross sectional view of a system for positioning and bondinga nutplate to a substrate comprising at least one aperture according toone or more embodiments of the present disclosure.

FIG. 2 is a schematic view of a rigid tube of a system for positioningand bonding a nutplate to a substrate comprising at least one apertureaccording to one or more embodiments of the present disclosure.

FIG. 3 is a cross sectional view of a nutplate engagement fixture of asystem for positioning and bonding a nutplate to a substrate comprisingat least one aperture according to one or more embodiments of thepresent disclosure.

FIG. 4A is a schematic view of a heater of a system for positioning andbonding a nutplate to a substrate comprising at least one apertureaccording to one or more embodiments of the present disclosure.

FIG. 4B is a transparent view of a portion of a system for positioningand bonding a nutplate to a substrate comprising at least one apertureaccording to one or more embodiments of the present disclosureillustrating positioning of the heater.

FIG. 5 is a cross sectional view of the heater disposed in the nutplateengagement fixture of a system for positioning and bonding a nutplate toa substrate comprising at least one aperture according to one or moreembodiments of the present disclosure.

FIG. 6 is a detailed view of section A of FIG. 1 .

FIG. 7A is a schematic view of a temperature sensor retention fixtureattached to an open style nutplate of a system for positioning andbonding a nutplate to a substrate comprising at least one apertureaccording to one or more embodiments of the present disclosure.

FIG. 7B is a cross sectional view of a temperature sensor retentionfixture for attachment to an open style nutplate of a system forpositioning and bonding a nutplate to a substrate comprising at leastone aperture according to one or more embodiments of the presentdisclosure.

FIG. 8A is a transparent view of a temperature sensor retention fixtureattached to a dome style nutplate of a system for positioning andbonding a nutplate to a substrate comprising at least one apertureaccording to one or more embodiments of the present disclosure.

FIG. 8B is a cross sectional view of a temperature sensor retentionfixture for attachment to a dome style nutplate of a system forpositioning and bonding a nutplate to a substrate comprising at leastone aperture according to one or more embodiments of the presentdisclosure.

FIG. 9A is a transparent view of a temperature sensor retention fixtureattached to a dome style nutplate of a system for positioning andbonding a nutplate to a substrate comprising at least one apertureaccording to one or more embodiments of the present disclosure.

FIG. 9B is a cross sectional view of a temperature sensor retentionfixture for attachment to a dome style nutplate of a system forpositioning and bonding a nutplate to a substrate comprising at leastone aperture according to one or more embodiments of the presentdisclosure.

FIG. 10A is a cross sectional view of a temperature sensor retentionfixture for attachment to an open style nutplate comprising an extendedfloating nut element of a system for positioning and bonding a nutplateto a substrate comprising at least one aperture according to one or moreembodiments of the present disclosure.

FIG. 10B is a cross sectional view of a temperature sensor retentionfixture for attachment to an open style nutplate comprising an extendedfloating nut element of a system for positioning and bonding a nutplateto a substrate comprising at least one aperture according to one or moreembodiments of the present disclosure.

FIG. 11A is a cross sectional view of a temperature sensor retentionfixture for attachment to a dome style nutplate comprising an extendeddomed region of a system for positioning and bonding a nutplate to asubstrate comprising at least one aperture according to one or moreembodiments of the present disclosure.

FIG. 11B is a cross sectional view of a temperature sensor retentionfixture for attachment to a dome style nutplate comprising an extendeddomed region of a system for positioning and bonding a nutplate to asubstrate comprising at least one aperture according to one or moreembodiments of the present disclosure.

FIG. 11C is a cross sectional view of a temperature sensor retentionfixture for attachment to a dome style nutplate comprising an extendeddomed region of a system for positioning and bonding a nutplate to asubstrate comprising at least one aperture according to one or moreembodiments of the present disclosure.

FIG. 12 is a cross sectional view of a temperature sensor retentionfixture comprising a C-shaped clip for attachment to a nutplate of asystem for positioning and bonding a nutplate to a substrate comprisingat least one aperture according to one or more embodiments of thepresent disclosure.

FIG. 13 is a cross sectional view of a temperature sensor retentionfixture comprising a C-shaped clip for attachment to a nutplate of asystem for positioning and bonding a nutplate to a substrate comprisingat least one aperture according to one or more embodiments of thepresent disclosure.

FIG. 14 is a cross sectional view of attachment of a fishing fixture toa nutplate engagement fixture of a system for positioning and bonding anutplate to a substrate comprising at least one aperture according toone or more embodiments of the present disclosure.

FIG. 15 is a schematic view of a panel having an aperture for subsequentattachment to the nutplate according to one or more embodiments of thepresent disclosure.

FIG. 16 is a schematic view of the outer surface of a dome stylenutplate utilized in a system for positioning and bonding a nutplate toa substrate comprising at least one aperture according to one or moreembodiments of the present disclosure.

FIG. 17A is a top view of the outer surface of an open style nutplateutilized in a system for positioning and bonding a nutplate to asubstrate comprising at least one aperture according to one or moreembodiments of the present disclosure.

FIG. 17B is cross-sectional view of FIG. 17A.

FIG. 18 is a flow diagram for one embodiment of a method of positioningand bonding a nutplate to a substrate comprising at least one apertureaccording to one or more embodiments of the present disclosure.

DETAILED DESCRIPTION

Specific embodiments of the present application will now be described.The disclosure may, however, be embodied in different forms and shouldnot be construed as limited to the embodiments set forth in thisdisclosure. Rather, these embodiments are provided so that thisdisclosure will be thorough and complete, and will fully convey thescope of the subject matter to those skilled in the art.

Embodiments of the present disclosure are directed to systems forpositioning and bonding a nutplate to a substrate and methods that applylocalized heating through the body of the nutplate and into the bondingsurface (i.e., the adhesive bondline between a substrate and nutplate)to accelerate the cure time required to securely bond the nutplate ontothe substrate and the associated instrumentation and fixtures. Bondingsurface may alternatively be referenced as the bondline or adhesivebondline. As used herein, “localized heating” means focused heatingdirected to the bonding surface, and limiting heating of the surroundingenvironment, particularly the surrounding substrate, by placing theheating component in direct contact with the heat conducting metal ofthe nutplate. The direct contact with the heat conducting metal of thenutplate allows efficient heat transfer through conduction to theadhesive bonding surface of the nutplate. For illustration, we haveincluded a discussion of embodiments of the system for positioning andbonding a nutplate to a substrate, specifically, systems whereinnutplates are adhered to panels (e.g., aircraft panels).

Referring to the embodiment of FIG. 1 , a nutplate retention system 5for securing a nutplate 10 to a substrate is depicted. The depictedsubstrate is a panel 20. The nutplate retention system 5 enablesapplication of localized heating to accelerate the curing rate of theadhesively bonded nutplates. Specifically, focused heating is directedto the bonding surface 11 (i.e. the adhesive bondline between thenutplate 10 and the panel 20) via the metal nutplate, and heating of thesurrounding environment and particularly the substrate is limited byplacing the heating component in the interior of a tube that is indirect contact with the metal nutplate. The positioning of the heatingelement allows efficient heat transfer through heat conduction to thebonding surface 11 to cure the adhesive and bond the nutplate 10 to thepanel 20. Alternate non-localized heating methods, such as the use ofelectric heating blanket, hot air with heat gun, and inductive heatingon hardware on a metal substructure, will likely result in excessive ornon-localized heating of the panel 20 or substructure, which maycontinue to transfer heat into the adhesive at the bonding surface 11after a desirable cure state of the adhesive is achieved. The continuedtransfer of heat into the adhesive at the bonding surface 11 may resultin undesirable adhesive or substructure material properties (i.e.overcuring of adhesive). In addition, operating these alternate heatingmethods is especially challenging when there is limited space or accessto the back side portion of the structure where the nutplate 10 willreside during installation or repair, since the equipment needed for thealternate methods are generally bulky and may not be compatible with thelimited space available. Furthermore, the use of non-localized heatingmay cause potential safety hazard in an environment that has ignitableorganic vapor. Also, heating directly on the outer surface of the panelopposing the nutplate 10 to raise the bonding surface 11 temperature mayrequire excessive heating to achieve sufficient heat transfer throughthe panel 20. In addition, such approach may not be feasible as theouter surface may be formed from a composite panel with low thermalconductivity.

As shown in FIG. 1 the panel 20 comprises at least one aperture 25.Multiple apertures 25 are contemplated as shown in the embodiment ofFIG. 15 . Moreover, various materials are considered suitable for thepanel 20. For example and not by way of limitation, the panel 20 maycomprise ceramic, metal, plastic, aluminum, titanium, fiber reinforcedpolymer matrix composite, ceramic matrix composite, or combinationsthereof. The panel 20 may comprise two different material layersfastened together to form a single panel.

Referring to the embodiments of FIGS. 4B, 7A, 14, and 17 , the nutplate10 comprises a substantially U-shaped profile with an open top to forman open style nutplate 10A. The substantially U-shaped profile of theopen style nutplate 10A is formed from an open style nutplate flatregion 12 and two parallel flanges 14. In one embodiment, the open stylenutplate 10A comprise a threaded hole 17 within the floating nut element19 centrally located on the open style nutplate flat region 12.

Referring to the embodiments of FIGS. 1, 8A, 8B, 9A, 9B, and 16 , thenutplate 10 comprises a domed region 15 to form a dome style nutplate10B. The dome style nutplate 10B may also comprise a dome style nutplateflat region 16 adjacent the domed region 15 of the dome style nutplate10B. Further, the dome style nutplate 10B comprise a threaded hole 17centrally located on the dome style nutplate flat region 16 and disposedwithin the domed region 15.

The open style nutplate flat region 12 of the open style nutplate 10A orthe dome style nutplate flat region 16 of the dome style nutplate 10Bmay serve as the bonding surface 11 for the open style nutplate 10A orthe dome style nutplate 10B respectively.

Various adhesives are considered suitable in the present embodiments,such as epoxy adhesives, acrylic adhesives, polyurethane adhesives orother adhesives known to the person skilled in the art.

Referring to FIG. 1 , the nutplate retention system 5 comprises anutplate engagement fixture 30. The nutplate engagement fixturecomprises a rigid tube 40 and an elastomeric tube 50. The rigid tube 40is operable to engage the nutplate 10 at one end and extend through oneaperture 25 of the panel 20. The elastomeric tube 50 is engaged with therigid tube 40 and configured to anchor the nutplate engagement fixture30 at the aperture 25 and secure the nutplate 10 in contact onto thepanel 20.

Additionally, the nutplate retention system 5 comprises a heater 60 thatdelivers heat to the bonding surface 11 of the nutplate 10 to acceleratethe cure of adhesive. In one or more embodiments, the heater 60 isoperable to be coaxially disposed within the nutplate engagement fixture30. Without being bound by theory, placing the heater 60 in contact withthe interior surface of the rigid tube 40 of the nutplate engagementfixture 30 enables heat to be locally delivered to the adhesive betweenthe nutplate 10 and panel 20 at the bonding surface 11 via heatconduction through the nutplate 10. By providing localized heat to thebonding surface 11, the concerns of providing heat in environments withflammable liquids or vapor is reduced or eliminated.

With continued reference to FIG. 1 , the nutplate retention system 5also comprises at least one temperature sensor 70 operable to measurethe temperature of the bonding surface 11 of the nutplate 10. In oneembodiment, the temperature sensor is a thermocouple. In anotherembodiment, the temperature sensor is a thermistor or resistancetemperature detector (RTD). The at least one temperature sensor 70 maybe retained in position with a temperature sensor retention fixture 80.The temperature sensor retention fixture 80 is operable to position andsecure the at least one temperature sensor 70 to the nutplate 10 duringthe cure.

The nutplate retention system 5 also comprises a heater controller 90operable to control the output from the heater 60. The heater controller90 may receive input signals from the at least one temperature sensor 70and adjust the output from the heater 60 to achieve or maintain adesired temperature at the bonding surface 11 of the nutplate 10.

Having introduced various components of the nutplate retention system 5,each component will be described and disclosed in further detail and asvarious embodiments.

The rigid tube 40 provides an engagement with the nutplate 10 to allowthe nutplate 10 to be positioned and restrained against the panel 20 bythe nutplate engagement fixture 30 during adhesive bonding of thenutplate 10 and the panel 20. With reference to FIGS. 2 and 3 , therigid tube may comprise a first section having a first diameter and asecond section having a second diameter, where the first diameter isgreater than the second diameter. The first section having the firstdiameter may comprise external threads 42 to form an externally threadedsection. The external threads 42 may be sized and configured to matewith the threaded hole 17 of the nutplate 10. It will be appreciatedthat while aircraft typically have nutplate sized from 3/16 inch to ½inch. As such, embodiments of the present disclosure may be configuredto engage with nutplate sized at 3/16 inch, ¼ inch, ⅜ inch, or ½ inch,for example.

The rigid tube 40 may also comprise an elastomeric tube retentionshoulder 44 positioned on the second section. The elastomeric tuberetention shoulder 44 comprises a circumferentially disposed lip on theexterior surface of the rigid tube 40 sized and configured to interfacewith a corresponding circumferentially disposed lip on the interiorsurface of the elastomeric tube 50.

In one or more embodiments, the rigid tube 40 comprises an internallythreaded section with internal threads 46. The internal threads 46 arepositioned proximal the end of the rigid tube 40 in the first section ina position concentric to the external threads 42. The internal threads46 may be provided with an opposite handedness as those of the externalthreads 42. Specifically, the external threads 42 may be provided withthe more common right-handed threads and the internal threads 46 may beprovided with left-handed threads.

Opposite handedness threads aid in the safe removal of a threaded insert(e.g. the rigid tube 40) from bonded hardware (e.g. the nutplate 10)after securement of the bonded hardware is completed. A threaded removaltool, with a thread direction matching the threaded insert's internalthreads, can be installed into the threaded insert. As the threadedinstallation tool engages the threaded insert and begins to generatetorque on the threaded insert, the threaded insert is simultaneouslyremoved from the bonded hardware by disengaging the threaded insert'sexternal threads. These design features ensure the threaded insertremains attached to the removal tool and does not become foreign objectdebris (FOD).

As used herein, “rigid tube” means an inflexible material and is incontrast to the rubbery “elastomeric tube” as described below. Inaddition, the rigid tube may be open at both ends or may have the firstsection with external threads being a closed end. In one or moreembodiments, the rigid tube 40 comprises a material with good thermalconductivity. In one or more embodiments, the rigid tube 40 comprises athermally conductive material with good thermal conductivity. Suchthermally conductive material may be metal or ceramic. For purposes ofthis disclosure, good thermal conductivity is considered to be in excessof 20 W/mK. In various embodiments the thermal conductivity of the rigidtube may be from 20-200 W/mK, from 50-200 W/mK, at least 50 W/mK, and atleast 100 W/mK. Various metals are contemplated as suitable, forexample, aluminum, copper, or stainless steel. Various ceramic arecontemplated as suitable, for example, silicon carbide, aluminumnitride, or magnesium oxide.

The elastomeric tube 50 is engaged with the rigid tube 40 and provides aresistance fit with the aperture 25 of the panel 20 to secure thenutplate 10 in contact with the panel 20 and secure the heater 60 incontact with the nutplate 10. With reference to FIG. 3 , the elastomerictube 50 comprises an elongated tube with an internal diameter sized toretain the heater 60 and an external diameter sized to provide afriction fit with the aperture 25 and retain the elastomeric tube 50 inposition.

In one or more embodiments, the external diameter of the elastomerictube 50 varies along a longitudinal length. Specifically, theelastomeric tube 50 may comprise a flared section 52 with an increasedexternal diameter. The flared section 52 may be disposed proximal theend of the elastomeric tube 50 configured for engagement with the rigidtube 40. The flared section 52 provides a compressive force and/orfriction fit with the aperture 25 when the elastomeric tube 50 isinserted therein to engage the nutplate engagement fixture 30 with thenutplate 10.

In one or more embodiments, the elastomeric tube 50 comprises aretention lip 54. The retention lip 54 comprises a section of reduceddiameter on the interior surface of the elastomeric tube 50 sized andconfigured to interface with the elastomeric tube retention shoulder 44on the exterior surface of the rigid tube 40.

In one or more embodiments, the elastomeric tube 50 may comprise a boss56 positioned at the end of the elastomeric tube 50 engaged with thenutplate 10. Specifically, the boss 56 provides a sealing interfacebetween the elastomeric tube 50, the bonding surface, and the nutplate10 to prevent adhesive migration into the threaded hole and onto theinternal threads of the nutplate 10. The boss 56 may extend into thethreaded hole 17 of the nutplate 10, such that a barrier is providedbetween a first interface of the bonding surface 11 and a secondinterface of the rigid tube 40 and the internal threads of the nutplate10. In addition, it also provide a barrier between the bonding surface11 and the aperture 25 of the panel 20 to prevent adhesive migrationinto the aperature 25.

Various materials are contemplated for the elastomeric tube 50 asdepicted in at least FIGS. 1 and 3 . These materials may includethermoplastic elastomer, thermosetting elastomer, or combinationsthereof. For example and not by way of limitation, the elastomer mayinclude one or more components selected from silicone rubber,polyurethane elastomer, fluoroelastomer, and perfluoroelastomer.

The heater 60 may encompass various embodiments. In one embodiment, theheater 60 comprises a joule heating element resided within a thermallyconductive cartridge 62. Various materials are contemplated for thejoule heating element, such as a nichrome wire. Additionally as shown inFIGS. 1, 4A, and 4B, the heater 60 may comprise a joule heating elementresided within a thermally conductive cartridge 62 connected to powerleads 65, which are connected to a power source. Various materials havebeen contemplated for the thermally conductive cartridge 62, includingmetal such as stainless steel, copper and aluminum, and ceramic such assilicon carbide, aluminum nitride and magnesium oxide. Any suitablepower source that may deliver current is contemplated. The power leads65 deliver current to the joule heating element within the thermallyconductive cartridge 62, which then produces the heat used to acceleratethe adhesive curing and bonding of the nutplate 10 to the panel 20.

The heater 60 may be retained in the nutplate engagement fixture 30 witha variety of mechanisms. Specifically, the heater 60 is operable todeliver heat to the bonding surface 11 of the nutplate 10 and isretained in a coaxially alignment within the nutplate engagement fixture30. With reference to FIGS. 4A and 4B, in one or more embodiments, theheater 60 comprises a heater extension 64. The heater extension 64increases the longitudinal length of the thermally conductive cartridge62 that contains the joule heating element. The heater extension 64 maybe affixed to the thermally conductive cartridge 62 with an adhesive,welding, or other securement method. The heater extension 64 may also bemachined as an integral part of the thermally conductive cartridge 62.The heater extension 64 allows the heater 60 to be accessed by aninstallation tool without interference from the elastomeric tube 50.Specifically, heater extension 64 provides access to manipulate thethermally conductive cartridge 62 such that it may be threaded it intothe rigid tube 40 when the heater 60 is positioned inside theelastomeric tube 50.

The threaded region 66 may be provided with threads matching the size,handedness, and pitch of the internal thread 46 of the rigid tube 40. Assuch, the heater 60 may be threadably engaged with the rigid tube 40 tosecure and retain the heater 60 in position for adhesive curing andbonding of the nutplate 10 to the panel 20. In addition, the threadablyengaged interface provides efficient heat transfer between the heater 60and the rigid tube 40. Further, the heater extension 64 may comprise ahex head 68 or other non-circular geometry to interface with a tool toallow rotational manipulation of the heater 60 into the rigid tube 40and subsequent removal. The tool may be a standard wrench or maycomprise a custom wrench with a central bore allowing passage of thepower leads 65 there through during manipulation.

In various embodiments, the heater 60 is removable from the nutplateengagement fixture 30. In one embodiment, the heater 60 is a cartridgeheater, which comprises a heating element within an enclosed heatconducting cartridge. Additional material such as thermal grease may beapplied to the interface between the heater 60 and the inside of therigid tube 40 to increase the efficiency of heat transfer between thetwo components.

With reference to FIG. 5 , in one or more embodiments, the heater 60 isretained in the nutplate engagement fixture 30 by a shoulder 63 on theheater 60 providing an area of increased diameter for engagement withthe elastomeric tube 50. The shoulder 63 provides a resistance orfriction fit against the elastomeric tube 50 as the diameter of theshoulder 63 is greater than the internal diameter of the elastomerictube 50. It will be appreciated that the greater the disparity betweenthe diameter of the shoulder 63 and the internal diameter of theelastomeric tube 50, the greater the resulting resistance forlongitudinal translation and placement of the heater 60 within theelastomeric tube 50 as the elastomeric tube 50 must be stretched ordeformed to a greater magnitude. Similarly, the longer the length of theshoulder 63, the greater the resulting resistance for longitudinaltranslation and placement of the heater 60 within the elastomeric tube50 as a greater length of the elastomeric tube 50 must be stretched. Theshoulder 63 may comprise a tapered or beveled edge at one or both endsof its longitudinal length to assist in placement of the heater 60within the elastomeric tube 50 and removal from the same.

With reference to FIG. 6 , in one or more embodiments, the heater 60 isretained in the nutplate engagement fixture 30 by mating shoulders onthe exterior diameter of the heater extension 64 and the interiordiameter of the elastomeric tube 50, with the exterior diameter of theheater extension 64 being greater than the interior diameter of theelastomeric tube 50. Specifically, the heater extension 64 has a taperedenlarged shoulder to minimize installation resistance when inserted intothe elastomeric tube 50. In addition, a heater extension shoulder 67 onthe heater extension 64 may engage an elastomeric tube shoulder 58having a complementary geometry. The heater extension shoulder 67 may beat a position proximal the junction with the heater cartridge 62. Theelastomeric tube shoulder 58 may be at a position such that, uponinsertion of the heater 60 into the nutplate engagement fixture 30, theheater extension shoulder 67 passes by and engages the elastomeric tubeshoulder 58 immediately prior to abutment of the heater extension 64against the rigid tube 40. As such, the heater 60 is held firmly inplace by the elastomeric tube shoulder 58 with the heater extensionshoulder 67 preventing backing out of the heater 60 from the nutplateengagement fixture 30.

In order to accurately monitor the heat curing temperature of thebonding adhesive and ensure appropriate cure profile is executed by aheater controller 90, at least one temperature sensor 70 is provided.The temperature sensor 70 may be positioned securely near a bondingsurface 11 of the nutplate 10. The temperature data obtained from the atleast one temperature sensor 70 can be logged and provide a feedbackmechanism for the heater controller 90 to manage the heating powersupplied to the heater 60. The heater controller 90 also may trigger oneor more fail-safe mechanisms built in to the heater controller 90 toprevent excessive power draw above the rated capacity of the heater 60,heater temperature above the rated operating range of the heater 60,excessive substrate temperature, or excessive nutplate surfacetemperature.

The temperature sensor retention fixture 80 is operable to position andsecure the at least one temperature sensor 70 to the nutplate 10. Itwill be appreciated that different and distinct styles of nutplates 10including open style nutplates and dome style nutplates may entail usageof distinct styles of the temperature sensor retention fixture 80. Forall styles of the temperature sensor retention fixture 80, passageways82 are provided within the structure of the temperature sensor retentionfixture 80 into which temperature sensor 70 and any associated wires maybe embedded. The rigid design of the temperature sensor retentionfixture 80 and the precise positioning of the temperature sensors 70within the passageways 82 allows for consistent contact between the atleast one temperature sensor 70 and the nutplate 10 at precisely definedlocations.

With reference to FIGS. 7A and 7B, in one or more embodiments, thetemperature sensor retention fixture 180 is configured for mating withthe open style nutplate 10A. The temperature sensor retention fixture180 comprises parallel arms 188 sized to nest within the parallelflanges which are complementary on the open style nutplate 10A.

In one or more embodiments, the temperature sensor retention fixture 180may comprise a threaded attachment element 184 configured for engagementwith the external threads 42 of the rigid tube 40. Engagement with theexternal threads 42 of the rigid tube 40 serves to secure thetemperature sensor retention fixture 180 to the open style nutplate 10Ato allow contact of the at least one temperature sensor 70 with the openstyle nutplate 10A. Specifically, the temperature sensor retentionfixture 180 allows for a threaded connection with the nutplateengagement fixture 30 to provide a secure connection until the rigidtube 40 is removed following curing of the adhesive utilized to securethe nutplate 10 to the panel 20.

With reference to FIGS. 8A, 8B, 9A, and 9B, in one or more embodiments,the temperature sensor retention fixture 280 is configured for matingwith a dome style nutplate 10B. The temperature sensor retention fixture280 comprises a body 282 enveloping the domed region 15 of the domestyle nutplate 10B. The body 282 may form a snug friction fit with thedome style nutplate 10B and allow contact of the at least onetemperature sensor 70 with the dome style nutplate 10B. Specifically,the body 282 forms a snap-in feature that fits snugly onto the outercontour of the dome style nutplate 10B.

With reference to FIGS. 7A, 7B, 8A, and 8B, in one or more embodimentsthe temperature sensor retention fixture 80 (180/280/380/480/580) maycomprise a tethering element 120 for retrieval of the temperature sensorretention fixture 80 and temperature sensors 70 after curing of theadhesive. The tethering element 120 may comprise a flexible cordconnected to the temperature sensor retention fixture 80 at the tethermounting point 86 which allows operators to safely reclaim thetemperature sensor retention fixture 80 and temperature sensors 70 oncethe nutplate 10 is securely bonded to the panel 20. The tether mountingpoint 86 may comprise a threaded hole to accept and engaged acomplementary threaded end on the tethering element 120. The tether mayalso be friction fit, or permanently affixed by adhesive bonding orplastic welding to the temperature sensor retention fixture 80 at thetether mounting point 86. While the tether mounting point 86 isgenerally shown in FIGS. 7A, 7B, 8A, and 8B as centrally located on thetemperature sensor retention fixture 80, it will be appreciated that thetether mounting point 86 may be positioned at any location on thetemperature sensor retention fixture 80 which does not interfere withthe coupling of the temperature sensor retention fixture 80 to thenutplate 10.

The temperature sensor retention fixture 80 may comprise a releaseactuator configured to disengage the temperature sensor retentionfixture 80 from the nutplate 10 upon actuation.

With reference to FIGS. 8A and 8B, in one or more embodiments, therelease actuator may be encompassed in the tethering element 120.Specifically, the temperature sensor retention fixture 280 comprises aflexible cable mounted at the tether mounting point 86 with the releaseactuator formed as part of the tethering element 120. In one or moreembodiments, the tethering element 120 may comprise a Bowden cable. Itwill be appreciated by one skilled in the art that a Bowden cable is atype of flexible cable used to transmit mechanical force or energy bythe movement of an inner cable relative to a hollow outer cable housing.In such embodiments, the tether mounting point 86 may be positioned withan end of the tethering element 120 engaged with the nutplate 10 suchthat upon activation of an engaging force with the Bowden cable thenutplate 10 is disengaged from the temperature sensor retention fixture280.

With reference to FIGS. 9A and 9B, in one or more embodiments, thetemperature sensor retention fixture 280 may also comprise a centralpiston 284 serving as the release actuator. The central piston 284 maybe configured to apply a force to disengage the temperature sensorretention fixture 280 from the dome style nutplate 10B upon activation.The central piston 284 may be disposed in a channel 286 allowing axialtravel of the central piston 284. In one or more embodiments, thecentral piston 284 and the channel 286 comprise complementary flanges orshoulders 285/287 configured to prevent travel of the central piston 284beyond the channel 286.

In one or more embodiments in combination with the central piston 284, asealing member 288 may be provided in a circumferential channel on thecentral piston 284. The sealing member 288 provides a seal between thecentral piston 284 and the channel 286. The sealing member 288 maycomprise an elastomeric material. Further, the sealing member 288 maycomprise an o-ring or other commercially available seal sized to providea tight fit with the circumferential channel on the central piston 284and the channel 286 formed in the body 282.

With continued reference to FIGS. 9A and 9B, in one or more embodimentsthe temperature sensor retention fixture 280 comprises a pneumaticrelease cable 292. The pneumatic release cable 292 triggersdisengagement of the temperature sensor retention fixture 280 from thenutplate 10. The pneumatic release cable 292 may be connected to thetemperature sensor retention fixture 280 in fluid communication with thecentral piston 284 of the temperature sensor retention fixture 280. Thepneumatic release cable 292 is configured to provide a pneumatic forceto the central piston 284 to disengage the temperature sensor retentionfixture 280 from the nutplate 10 upon activation. It will be appreciatedthat the central piston may also be activated as a piezoelectric orother mechanical actuator, with the pneumatic scenario of the presentdisclosure being provided as an example. In one or more embodiments, thepneumatic release cable 292 may be the tethering element 120.Specifically, the pneumatic release cable 292 may be connected to thetemperature sensor retention fixture 280 via a threaded or bondedconnection where the pneumatic release cable 292 comprising externalthreads configured for engagement with the tether mounting point 86 ofthe temperature sensor retention fixture 280. Further, the fluidcommunication between the pneumatic release cable 292 and the centralpiston 284 may be provided via an airflow passage 294 connecting thetether mounting point 86 and the channel 286.

The pneumatic release cable 292 may be a flexible tube capable ofpassage of pressurized air therethrough. In various embodiments, thepneumatic release cable 292 is comprised of a flexible plastic tube, aflexible braided conduit, or a flexible elastomer tube. The pneumaticrelease cable 292 allows air to pass through and is flexible such thatis can fit into tight spaces and around tight bends.

With reference to FIGS. 10A and 10B, in one or more embodiments, thetemperature sensor retention fixture 380 may be configured toaccommodate open-style nutplates 10A comprising an extended floating nutelement 19. Specifically, the temperature sensor retention fixture 380may comprise a centrally located hole 390 sized to accommodate passageof the floating nut element 19 such that the temperature sensorretention fixture 380 may nest on the open-style nutplate 10A with thefloating nut element 19 passing through the centrally located hole 390.

The temperature sensor retention fixture 380 configured to accommodateopen-style nutplates 10A comprising an extended floating nut element 19may additionally comprise at least one peripheral piston 384 positionedat the bottom of the temperature sensor retention fixture 380 adjacentto the nutplate flat region 12 serving as the release actuator. The body382 may form a snug friction fit with the extended floating nut element19. The peripheral piston 384 may be connected to the pneumatic releasecable 292 via a pneumatic inlet 386 and air channels 388 such that thepneumatic release cable 292 may trigger disengagement of the temperaturesensor retention fixture 380 from the nutplate 10 upon activation of theperipheral piston 384. Specifically, the pneumatic release cable 292 maybe connected to the temperature sensor retention fixture 380 providingfluid communication with the peripheral piston 384 of the temperaturesensor retention fixture 380 such that provision of compressed airwithin the pneumatic release cable 292 forces the peripheral piston 384to extend. The extension of the peripheral piston 384 applies a force tothe nutplate flat region 12 forcing separation of the nutplate 10 andthe temperature sensor retention fixture 380. It will be appreciatedthat the peripheral piston 384 may also be activated as a piezoelectricor other mechanical actuator, with the pneumatic scenario of the presentdisclosure being provided as an example.

Similar to the temperature sensor retention fixture 380 configured fortall open style nutplates 10A, a temperature sensor retention figures480 may be configured for interfacing with tall domed style nutplates10B. With reference to FIGS. 11A, 11B, and 10C, in one or moreembodiments, the temperature sensor retention fixture 480 may beconfigured to accommodate dome-style nutplates 10B comprising anextended domed region 15. Specifically, the temperature sensor retentionfixture 480 may comprise a centrally located hole 490 sized toaccommodate passage of the domed region 15 such that the temperaturesensor retention fixture 480 may nest on the dome-style nutplate 10Bwith the domed region 15 passing through the centrally located hole 490.

The temperature sensor retention fixture 480 configured for engagementwith a tall dome style nutplate 10B may additionally comprise at leastone peripheral piston 484 positioned at the bottom of the temperaturesensor retention fixture 480 adjacent to dome style nutplate flat region16 serving as the release actuator. The peripheral piston 484 may beconnected to the pneumatic release cable 292 via a pneumatic inlet 386and air channels 388 such that the pneumatic release cable 292 maytrigger disengagement of the temperature sensor retention fixture 480from the nutplate 10 upon activation of the peripheral piston 484.Specifically, the pneumatic release cable 292 may be connected to thetemperature sensor retention fixture 480 providing fluid communicationwith the peripheral piston 484 of the temperature sensor retentionfixture 480 such that provision of compressed air within the pneumaticrelease cable 292 forces the peripheral piston 484 to extend. Theextension of the peripheral piston 484 applies a force to the dome stylenutplate flat region 16 forcing separation of the nutplate 10 and thetemperature sensor retention fixture 480. It will be appreciated thatthe peripheral piston 484 may also be activated as a piezoelectric orother mechanical actuator, with the pneumatic scenario of the presentdisclosure being provided as an example.

The open top design of the temperature sensor retention fixtures 380 and480 with the floating nut element 19 and the domed region 15 of thenutplate 10 respectively projecting therethrough minimizes the totalheight of the assembly of the nutplate 10 and the temperature sensorretention fixture 380/480. Minimizing total height assists in successfulinstallation of tall nutplates 10 onto panels 20 within tight spacessuch as within a confined aircraft substructure.

With reference to FIGS. 12 and 13 , in one or more embodiments, thetemperature sensor retention fixture 580 comprises a C-shape clip with adisengagement piston 584 positioned adjacent to the cylindrical exteriorwall of the floating nut element 19 or domed region 15 serving as therelease actuator. The temperature sensor retention fixture 580 issecured onto the floating nut element 19 of the open style nutplate 10Aor the domed region 15 of the dome style nutplate 10 with a snugclamping fit. Specifically, the temperature sensor retention fixture 580comprises a snap-in gripping feature that fits snugly onto the externalwall contour of the floating nut element 19 or domed region 15. Withreference to FIG. 17 in particular, the C-shape clip may be providedwith a two-piece construction and with a torsion spring hinge mechanism596 connecting the two pieces. For removal of the temperature sensorretention fixture 580 from the nutplate 10, the disengagement piston 584may be connected to the pneumatic release cable 292. The pneumaticrelease cable 292 triggers disengagement of the temperature sensorretention fixture 580 from the nutplate 10 by extending thedisengagement piston 584 and forcing separation of the temperaturesensor retention fixture 580 and the floating nut element 19 or thedomed region 15 of the open style nutplate 10A and dome style nutplate10B respectively. It will be appreciated that the disengagement piston584 may also be activated as a piezoelectric or other mechanicalactuator, with the pneumatic scenario of the present disclosure beingprovided as an example.

With reference to FIG. 18 , in one or more embodiments, the nutplateretention system 5 comprises a fishing fixture 110 for positioning anutplate installation assembly 100 comprising the nutplate 10, thenutplate engagement fixture 30, and the temperature sensor retentionfixture 80 onto the panel 20. Access to both sides of the panel 20during installation of the nutplate 10 is not always readily available.Specifically, the apertures 25 of the panel 20 may be positioned suchthat they are not within the reach of an arm because of distance or sizerestrictions from the structure underlying the panel 20. As such, thefishing fixture 110 allows a cable 112 to be passed through the interiorstructure underlying the panel 20 and affixed to the elastomeric tube 50with a securement plug 114. The cable 112 may be affixed to thesecurement plug through any means known to one skilled in the artincluding adhesive or a threaded connection. The securement plug 114 maybe removably secured to the elastomeric tube 50 with a friction fit.Specifically, the securement plug 114 may comprise a cylindricalgeometry with a diameter larger than the interior diameter of theelastomeric tube 50 such that the securement plug 114 may be insertedinto the elastomeric tube 50 with a commensurate stretching of thediameter of the elastomeric tube 50 providing a retentive force. Afteraffixing the fishing fixture 110 to the elastomeric tube 50, the entirenutplate installation assembly 100 may be pulled with the cable 112through the interior structure underlying the panel 20 to position thenutplate 10 in alignment with the aperture 25 on an interior face of thepanel 20 that is inaccessible by hand.

In one or more embodiments, the securement plug 114 includes a conicalfrustum 116 at the end of the securement plug 114 comprising attachmentof the cable 112. The conical frustum 116 provides a flat surface uponwhich a hole may be provided for attachment of the cable 112. Further,the conical frustum 116 provides a tapered geometry at the leading edgeof the securement plug 114 during passage through the aperture 25 of thepanel 20. Specifically, the tapered geometry assists in aligning andcentering the securement plug 114 to facilitate the passage of theaffixed elastomeric tube 50 through the aperture 25. In one or moreembodiments, the conical frustum 116 also comprises a diameter at thebase greater than the diameter of the remainder of the securement plug114, thereby providing a circumferential ledge. The circumferentialledge may provide a stop against the elastomeric tube 50 upon fullinsertion of the securement plug 114.

In one or more embodiments, the securement plug 114 includes a taperededge 118 around the periphery of the end of the securement plug 114. Thetapered edge 118 assists with centering and aligning the securement plug114 with the interior of the elastomeric tube 50 during insertion of thesecurement plug 114 into the elastomeric tube 50.

With reference to FIG. 1 , in one or more embodiments, an exteriorsecurement washer 98 may optionally be incorporated into the bondedhardware installation process to improve safety and reliability. Theexterior securement washer 98 has a through-hole with a diameter sizedto substantially match the diameter of the apertures 25 in the panel 20.The exterior securement washer 98 may be passed over the elastomerictube 50 and positioned in a position abutting the panel 20. As such, theexterior securement washer 98 provides additional holding force throughfrictional interaction with the elastomeric tube 50 to retain thenutplate 10 in tension against the opposing surface of the panel 20. Inone or more embodiments, at least one passageway 99 is provided withinthe structure of the washer into which a temperature sensor 70 may beembedded.

To position the exterior securement washer 98, prior to inserting theheater 60 into the elastomeric tube 50, the exterior securement washer98 is installed around the elastomeric tube 50 and positioned onto theexterior surface of the panel 20, opposite the adhesive bonding surface11. Installing the exterior securement washer 98 is accomplished bypulling on the elastomeric tube 50 which reduces in diameter whensubjected to tensile load (i.e. Poisson's effect) to allow passage ofthe exterior securement washer 98 along the length of the elastomerictube 50. Once in position the tensile force can be relieved from theelastomeric tube 50 thereby expanding the elastomeric tube 50 indiameter and producing an interference fit with the through-hole of theexterior securement washer 98. For additional temperature feedback andcontrol the temperature sensor 70 can be positioned within thepassageway 99 or affixed to the surface of the exterior securementwasher 98 abutting the panel 20 prior to installation on the elastomerictube 50. Once the exterior securement washer 98 is installed onto thepanel 20, the temperature sensor 70 is made to contact the panel 20 onthe exterior surface opposite the adhesive bonding surface 11, providinga measure of the temperature of the panel 20 surface.

Turning from the above discussion of components of the nutplateretention system 5, the following discussion relates to the utilizationof these components in processes for adhering a nutplate 10 to a panel20. In one or more embodiments, the method comprises assembling thenutplate engagement fixture 30 by coupling the rigid tube 40 with theelastomeric tube 50, coupling the nutplate 10 with the nutplateengagement fixture 30, coupling the fishing fixture 110 to theelastomeric tube 50, coupling the temperature sensor retention fixture80 to the nutplate 10, applying adhesive onto the bonding surface 11 ofthe nutplate 10, inserting the nutplate engagement fixture 30 through anaperture 25 of the panel 20 until a surface of the panel 20 contacts thebonding surface 11 having adhesive applied thereon, and adhering thenutplate 10 to the bonding surface of the panel 20 by applying localizedheat through a heater 60 disposed within the nutplate engagement fixture30. Finally, the method further comprises removing the heater 60, thenutplate engagement fixture 30, and the temperature sensor retentionfixture 80 from the nutplate 10 after the adhering step.

Referring to FIG. 3 , the nutplate engagement fixture 30 is assembled bycoupling the rigid tube 40 with the elastomeric tube 50 (FIG. 18 , step610). Specifically, the rigid tube 40 is pressed into the elastomerictube 50 so that the elastomeric tube retention shoulder 44 on the rigidtube 40 is engaged with the retention lip 54 of the elastomeric tube 50.Alternatively, the nutplate engagement fixture 30 may be assembled byover-molding of the elastomeric tube 50 onto rigid tube 40 in amanufacturing environment.

The nutplate 10 is then coupled with the nutplate engagement fixture 30to form subassembly I (FIG. 18 , step 620). In one or more embodiments,the nutplate 10 and the nutplate engagement fixture 30 may be coupled bythreading the rigid tube 40 of the nutplate engagement fixture 30 intothe threaded hole 17 of the nutplate 10.

In one or more embodiments, the fishing fixture 110 is also affixed tothe elastomeric tube 50 of the nutplate engagement fixture 30 (FIG. 18 ,step 630). The fishing fixture 110 is attached to the nutplateengagement fixture 30 by inserting the securement plug 114 into the freeend of the elastomeric tube 50. The securement plug 114 is retained inthe elastomeric tube 50 with a friction fit provided by the compressiveforce of the elastomeric tube 50 stretched around the securement plug114. It will be appreciated that attachment of the fishing fixture 110is not necessary when ample access is available to position subassemblyI without the aid of the fishing fixture 110.

The temperature sensor retention fixture 80 is then coupled with thenutplate 10 to form subassembly II alternatively referenced as thenutplate installation assembly 100 (FIG. 18 , step 640). Subassembly IImay include solely the temperature sensor retention fixture 80 andsubassembly I or additionally the fishing fixture 110. With reference toFIGS. 7A and 7B, in one or more embodiments comprising the open stylenutplate 10A, the temperature sensor retention fixture 80 is coupledwith the open style nutplate 10A by advancing the rigid tube 40 suchthat the external threads 42 on the rigid tube 40 engage with thethreaded attachment element 184 of the temperature sensor retentionfixture 180. With reference to FIGS. 8A, 8B, 9A, and 9B, in one or moreembodiments comprising the dome style nutplate 10B, the temperaturesensor retention fixture 280 is coupled with the dome style nutplate 10Bby pressing the temperature sensor retention fixture 280 over the domedregion 15 of the dome style nutplate 10B to engage the snap-fit orfriction fit of the temperature sensor retention fixture 280 thereto.

Subsequently, the adhesive is applied to the nutplate 10 (FIG. 18 , step650) and subassembly II of the nutplate retention system 5, as shown inFIG. 14 , is then fed through the aperture 25 of the panel 20 (FIG. 18 ,step 660). Specifically, the elastomeric tube 50 is fed through theaperture 25 and pulled taut to engage the flared section 52 of theelastomeric tube 50 with an increased external diameter. It will beappreciated that the flared section 52 provides a compressive forceand/or friction fit with the aperture 25 when the elastomeric tube 50 isinserted into the aperture 25. Further, engaging the flared section 52concurrently draws the nutplate 10 against panel 20 allowing theadhesive to spread across the bonding surface 11 until the desiredbondline thickness is achieved.

After engagement of subassembly II with the aperture 25, the fishingfixture 110, if present and utilized, is removed (FIG. 18 , step 670).The fishing fixture 110 may be removed from the elastomeric tube 50 byrestraining the elastomeric tube 50 and applying a pulling force to thecable 112 or directly to the securement plug 114 to overcome thecompressive force of the elastomeric tube 50 on the securement plug 114.

The exterior securement washer 98 with embedded temperature sensors 70may optionally be installed onto the subassembly II by inserting theelastomeric tube 50 through the through-hole on the exterior securementwasher 98. The exterior securement washer 98 is then secured onto thepanel 20 by pulling on the elastomeric tube 50. Once in position, thetensile force can be reduced on the elastomeric tube 50, which expandsin diameter and produces an interference fit with the through-hole ofthe exterior securement washer 98.

The heater 60 is then inserted into the interior of the nutplateengagement fixture 30 (FIG. 18 , steps 680). With reference to FIGS. 4Aand 4B, in one or more embodiments, the heater 60 is retained in thenutplate engagement fixture 30 with the threaded region 66 at the tip ofthe heater 60. Specifically, the heater 60 may be threadably engagedwith the rigid tube 40 to secure and retain the heater 60 in positionfor curing of the nutplate 10 to the panel 20. In embodiments where theheater extension 64 of the heater 60 comprises a hex head 68 or othernon-circular geometry a tool may be used to interface with the heaterextension 64 to allow screwing of the heater 60 into the rigid tube 40and subsequent removal. With reference to FIG. 5 , in one or moreembodiments, the heater 60 is retained in the nutplate engagementfixture 30 by the shoulder 63 on the heater 60 which provides aresistance or friction fit against the elastomeric tube 50 as thediameter of the shoulder 63 is greater than the internal diameter of theelastomeric tube 50. With reference to FIG. 6 , in one or moreembodiments, the heater 60 is retained in the nutplate engagementfixture 30 by engaging the heater extension shoulder 67 on the heaterextension 64 with the complementary geometry of the elastomeric tubeshoulder 58. Specifically, upon insertion of the heater 60 into thenutplate engagement fixture 30, the heater extension shoulder 67 passesby and engages the elastomeric tube shoulder 58 immediately prior toabutment of the heater extension 64 against the rigid tube 40. As such,the heater 60 is held firmly in place with the elastomeric tube shoulder58 and the heater extension shoulder 67 preventing backing out of theheater 60 from the nutplate engagement fixture 30.

Upon engagement and securing of the heater 60 in the nutplate engagementfixture 30, curing of the adhesive is begun (FIG. 18 , step 690). Therapid cure process may be carried out by operating the heater controller90 to deliver resistive heating via the heater 60 at the bonding surface11. The heater controller 90 may further monitor and regulate theheating profile over the rapid cure process through a feedback mechanismwith the use of the temperature sensors 70. The heater controller 90comprises microprocessor, temperature and power controllers, data inputoutput ports, and the one or more temperature sensors 70.

Further, referring to FIG. 18 , after the curing step, which may occurfor 1 to 6 hours, the heater 60 may be removed from the nutplateengagement fixture 30 and the nutplate engagement fixture 30 maysubsequently be removed from the nutplate 10 (FIG. 18 , step 700) whichhas been bonded to the panel 20. In one or more embodiments, removingthe heater 60 from the nutplate engagement fixture 30 comprisesunthreading the threaded region 66 at the tip of the heater 60 from therigid tube 40 and withdrawing the heater 60 from the nutplate engagementfixture 30. In one or more further embodiments, removing the heater 60comprises applying a withdrawing force to the heater to overcome theresistance or friction fit between the shoulder 63 on the heater 60 andthe internal diameter of the elastomeric tube 50. Similarly, in one ormore further embodiments, removing the heater 60 comprises applying awithdrawing force to the heater to overcome the engagement between theheater extension shoulder 67 and the elastomeric tube shoulder 58thereby allowing the heater 60 to be fully withdrawn from the nutplateengagement fixture 30.

In one or more embodiments, removing the nutplate engagement fixture 30is a two-step process. In a first step the elastomeric tube 50 isdisengaged from the rigid tube 40 by apply a force to overcome theengagement between the elastomeric tube retention shoulder 44 on therigid tube 40 that is engaged with the retention lip 54 of theelastomeric tube 50. In a second step the rigid tube 40 is disengagedfrom the nutplate 10 by unthreading the rigid tube 40 from the threadedhole 17 of the nutplate 10. The rigid tube 40 can be secured forunthreading by threading a tool into the internal threads 46 of therigid tube 40 as the internal threads 46 are provided with an oppositehandedness as those of the external threads 42 resulting in a tighteningaction on the internal threads 46 causing an opposite loosing action atthe external threads 42.

Finally, the temperature sensor retention fixture 80 is removed from thenutplate 10 and drawn out with the tethering element 120 (FIG. 18 , step710). In one or more embodiments with the open style nutplate 10A, thetemperature sensor retention fixture 180 may be disengaged from the openstyle nutplate 10A automatically upon removal of the rigid tube 40 asthe external threads 42 on the rigid tube 40 are disengaged from thethreaded attachment element 184 of the temperature sensor retentionfixture 180. A tugging force on the tethering element 120 may also berequired in some instances to release the temperature sensor retentionfixture 180 from the open style nutplate 10A after removal of the rigidtube 40 to overcome any friction forces retaining the temperature sensorretention fixture 180 in engagement with the open style nutplate 10A. Inone or more embodiments with the dome style nutplate 10B, thetemperature sensor retention fixture 280 may be disengaged from the domestyle nutplate 10B with application of compressed air to the pneumaticrelease cable 292. The pneumatic release cable 292 triggersdisengagement of the temperature sensor retention fixture 280 from thedome style nutplate 10B by actuating the central piston 284 of thetemperature sensor retention fixture 280 which is engaged with the domedregion 15 of the dome style nutplate 10B thereby forcing separation ofthe temperature sensor retention fixture 280 and the dome style nutplate10B. Similarly, in one or more embodiments with the dome style nutplate10B, the tethering element 120 may comprise a Bowen cable which isengaged with the domed region 15 of the dome style nutplate 10B therebyforcing separation of the temperature sensor retention fixture 280 andthe dome style nutplate 10B when activated.

In this accelerated cure process, the bulk of the material cure canoccur in a shortened timespan to the desirable cure state, but furtherundesired reactions from elevated temperature “post-cure” are avoided.Without being bound by theory, in a polymer material such as a two-partepoxy adhesive, the reaction of smaller precursor molecules (e.g.,monomers, pre-polymers) results in the growth of larger and increasingmolecular weight chains of the constituent molecules. If thepolymerization is allowed to proceed only at room temperature, theformation of networked polymer chains will gradually impede the mobilityof remaining reactive molecules, essentially slowing down and eventuallyarresting the polymerization and cure of the material to achievespecified polymer properties. At an elevated temperature, the mobilityof any remaining reactive molecules will be increased and thusincreasing the polymerization rate of the material, thus reducing thetime required to achieve a similar cure state comparing with curing atroom temperature.

In one or more embodiments, the process may also comprise preparing thesurface of the panel 20. This may involve cleaning the panel 20 surfaceto facilitate better adhesion once the nutplate 10 is adhesively bondedto the panel 20.

Additionally, to monitor the adhesive curing and bonding of the nutplate10 to the panel 20, a feedback temperature control mechanism may beutilized so that the desired temperature profile can be maintainedirrespective of panel material. The feedback temperature controlmechanism may include the at least one temperature sensor 70 incommunication with a controller. Various suitable controllers, such as apower controller, a temperature controller, are contemplated as long asthey can regulate specific parameters based on input from thetemperature sensor. A single controller 90 may interface with one ormultiple sets of the heater 60, the temperature sensor retention fixture80/180/280/380/480/580, and the nutplate engagement fixture 30. Inspecific embodiments, the controller for the temperature and the powersource for the heating component may be integrated into the same unit toform the feedback temperature control mechanism.

The nutplate retention system 5 may further comprise a digital recordretention system. The digital record retention system provides easilyretrievable records of installation parameters, maintenance history, andoperation status, including environmental conditions, on all nutplateparts in-situ on the substrate to facilitate logistic and maintenanceplanning. In one or more embodiments, digital record retention systemenables remote assessment of part status (for example, service hourhistory) or part curing status (for example, parameters of nutplateinstallation). Such digital record retention system also providesend-to-end traceability on parts and makes collected information readilyavailable to the technicians and engineers involved in logistic andmaintenance planning through computer networks, wireless networks,and/or mobile devices.

The digital record retention system comprises a writable storage mediumconfigured to record process parameters of the bonding of the nutplateto the substrate including environmental conditions at time of bonding,temperature readings from the at least one temperature sensor withrespect to time, and identifying codes assigned to each component of thesystem utilized in bonding of the nutplate to the substrate. In additionit can also record information related to the status of the nutplateretention system 5 such as power and error status. Specifically, theenvironmental conditions at time of bonding may include air temperatureand humidity levels at the location and time of nutplate adherence. Thetemperature readings from the at least one temperature sensor withrespect to time may also be recorded to provide a plot of adhesive andnutplate heating during the cure cycle. The temperature profile mayprovide insight to strength parameters of the bond and provide guidancein the event of bond failure or bonding process disruption such as powerfailure. Further, identifying codes assigned to each component of thenutplate retention system utilized in bonding of the nutplate to thesubstrate provides traceable history in the event of a bond failure. Forexample, unique serial numbers and/or identifying bar codes may beprovided on each nutplate, fixture, heater, adhesive and other componentused in the installation of the nutplate on the substrate to allowscanning and tracking for each step and variable of each individualnutplate installation event. The recording of the adhesive batch numberused on each nutplate installation allows for accounting of suspectnutplate installations in the event of later determination of faultyadhesive. Notes from technicians during nutplate installation or laterinspections may also be recorded to provide a more complete portfolio ofdata regarding the nutplate installation.

In one or more embodiments, the desired collected data points may bescanned or entered into the digital record retention system in real-timeduring nutplate installation. In some embodiments, the digital recordretention system and the heater controller may be combined into a singleintegrated system. An integrated system combines the heating andinstallation protocols with the data retention protocols into a singleunified system. The integrated nutplate installation and digital recordretention system in one or more embodiments may prompt the installationor maintenance technician to scan a barcode or input a serial numberduring installation or maintenance operations to develop a complete dataset for each nutplate installation event.

Depending on the maintenance location or field environment, the heatercontroller and digital record retention system may be a wall-poweredstation or a handheld, battery-powered, mobile unit. A battery poweredunit may also have corresponding charging station to carry ample supplyof charged batteries or power packs to minimize interruptions ofmaintenance operation.

It will be apparent that modifications and variations are possiblewithout departing from the scope of the disclosure defined in theappended claims. More specifically, although some aspects of the presentdisclosure are identified herein as preferred or particularlyadvantageous, it is contemplated that the present disclosure is notnecessarily limited to these aspects.

The invention claimed is:
 1. A system for positioning and bonding anutplate to a substrate comprising at least one aperture, the systemcomprising: a nutplate engagement fixture comprising a rigid tube,wherein the rigid tube is operable to engage the nutplate at one end andextend through one of the at least one apertures of the substrate; aheater coaxially disposed within the nutplate engagement fixture andoperable to deliver heat to a bonding surface of the nutplate; at leastone temperature sensor operable to measure the temperature of thebonding surface of the nutplate; a temperature sensor retention fixtureoperable to position and secure the at least one temperature sensor tothe nutplate; and a heater controller operable to control the heatdelivered by the heater.
 2. The system of claim 1, wherein the substrateis a panel.
 3. The system of claim 1, wherein the rigid tube comprisesexternal threads configured for threaded engagement with internalthreads on the nutplate.
 4. The system of claim 3, wherein the rigidtube further comprises an internally threaded section wherein theinternal threads have an opposite handedness as the external threads. 5.The system of claim 3, wherein the temperature sensor retention fixturecomprises a threaded attachment element configured for engagement withthe external threads of the rigid tube to secure the temperature sensorretention fixture to the nutplate and allow contact of the at least onetemperature sensor with the nutplate.
 6. The system of claim 1, whereinthe rigid tube further comprises an internally threaded section.
 7. Thesystem of claim 1, wherein the heater is a cartridge heater.
 8. Thesystem of claim 7, wherein the heater comprises exterior left-handedthreads for engagement with corresponding interior left-handed threadson the nutplate engagement fixture.
 9. The system of claim 1, whereinthe system further comprises a fishing fixture for positioning anutplate installation assembly comprising the nutplate, the nutplateengagement fixture, and the temperature sensor retention fixture ontothe substrate.
 10. The system of claim 1, wherein the temperature sensorretention fixture forms a friction fit with the nutplate and allowscontact of the at least one temperature sensor with the nutplate. 11.The system of claim 10, wherein the temperature sensor retention fixturecomprises at least one release actuator configured to apply a force todisengage the temperature sensor retention fixture from the nutplateupon activation.
 12. The system of claim 11, wherein the at least onerelease actuator comprises at least one piston and the temperaturesensor retention fixture comprises a pneumatic release cable for bothtriggering disengagement of the temperature sensor retention fixturefrom the bonded nutplate and temperature sensor retention fixtureretrieval, wherein the pneumatic release cable is connected to thetemperature sensor retention fixture in fluid communication with the atleast one piston of the temperature sensor retention fixture and isconfigured to provide a pneumatic force to the at least one piston todisengage the temperature sensor retention fixture from the nutplateupon activation.
 13. The system of claim 1, wherein the temperaturesensor retention fixture comprises a tethering element for fixtureretrieval.
 14. The system of claim 13, wherein the tethering elementcomprises a flexible cable mounted at a tether mounting point for bothtriggering disengagement of the temperature sensor retention fixture andtemperature sensor retention fixture retrieval, wherein the tethermounting point is positioned with an end of the flexible cable engagedwith the nutplate such that upon application of an engaging force withthe flexible cable the nutplate is disengaged from the temperaturesensor retention fixture.
 15. The system of claim 1, wherein the systemfurther comprises a digital record retention system, the digital recordretention system comprising: a writable storage medium configured torecord process parameters of the bonding of the nutplate to thesubstrate including the settings of the heater controller, environmentalconditions at time of bonding, temperature readings from the at leastone temperature sensor with respect to time, and identifying codesassigned to the nutplate and each component of the system of claim 1utilized in bonding of the nutplate to the substrate.